Many kinds of mechanical equipment utilize electrical sensors or transducers to provide electrical output signals for measuring parameters and/or identifying physical events such as the displacement of a movable part. For instance, modem internal combustion engine designs utilize Electronic Throttle Control (ETC) to adjust the fuel injection, the engine spark and the amount of airflow through an intake manifold of an engine in response to sensor monitored operator variations of a movable accelerator. Such ETC systems provide many advantages such as reduced costs, improved simplicity, reduced engine noise, throttle command conditioning for emissions reduction and/or torque based control functions. Operator adjustment of the accelerator position or displacement is typically accomplished through the use of an accelerator-input mechanism such as a foot pedal.
The accelerator input mechanism is mechanically coupled to multiple sensors that in turn provide output signals having magnitudes indicative of the accelerator position or displacement to an ETC microprocessor. The magnitudes of such sensor output signals are utilized by the microprocessor to generate control signals for enabling the hardware of the engine to provide the operating levels indicated by the positioning of the accelerator input mechanism. Multiple or “redundant” input sensors are presently utilized to sense a particular parameter such as the amount of accelerator pedal depression to improve sensing reliability. Redundant accelerator sensors of the same technology type and associated hardware have become standard in ETC systems with the multiple sensors being processed to ensure secure pedal and throttle signals.
ETC systems compute correlation errors to monitor the condition of the redundant accelerator sensors so that corrective action can be taken if a sensor is failing or has failed by opening up or shorting out for instance. A correlation error is a function of the difference in the instantaneous magnitudes of the output signals from the sensors. Some prior art ETC systems monitor and store the correlation error of such sensors only when the accelerator pedal is released, for instance. Thus a correlation error for these sensors is learned only at one accelerator position such as at idle when the throttle is closed. Accordingly the correlation error value is undesirably only intermittently monitored by such prior art systems to determine accelerator pedal sensor reliability.
Position sensors of reasonable cost provide sensor output signal magnitude variations that fall short of a major failure and thus have small correlation errors. Such variations can occur because of the drop in magnitude of a supply or reference voltage for at least one of the sensors that has nothing to do with the condition of the sensor but results from an increase in the electrical load on the supply, for example. Expensive prior art solutions include either providing separate and independent dedicated reference voltage supplies for each pedal sensor or providing a high precision common reference voltage supply. If the sensors of some prior art systems are configured to have characteristics with opposite slopes a change in the reference voltage can differently affect the outputs levels of the sensors thereby initiating false error codes.
Also normal wear and tear and manufacturing tolerances can cause sensors of the same type to perform differently to some extent over time. Accordingly some variation in the outputs of the sensors should be tolerated so that the foregoing corrective actions are not unnecessarily initiated. To address this problem some prior art systems require expensive sensors that are manufactured with restrictive tolerances so that their correlation errors are minimized. Other prior art systems require that three or more sensors be used to measure the same parameter so that a malfunctioning sensor can be identified because its output level is different from the output levels of the other sensors. Both of the foregoing solutions tend to be undesirably expensive.
In view of the foregoing, it should be appreciated that it is desirable to provide inexpensive methods and apparatus for providing continuous, accurate and reliable detection of redundant sensors to facilitate notification that a sensor either is failing or has failed. Moreover it is important that such systems be tolerant of acceptable correlation errors which can result from physical variations in the sensors and/or a minor fault in a sensor. This enables such sensors to have less restrictive tolerances. Thus the sensors can be less expensive than otherwise would be the case thereby facilitating the use of existing sensors. Furthermore, it is desirable that such methods and apparatus are relatively immune to disturbances, noise and/or temporary changes in the magnitude of the reference voltage for the sensors. It is further desirable that such methods and apparatus require either no or only minimal changes in the other portions of the overall system such as either wiring changes, or the redesign of presently used reference voltage supplies.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent brief summary, detailed description, appended claims, and abstract, taken in conjunction with the accompanying drawings and the foregoing technical field and background.